Lower psoas mass indicates worse prognosis in percutaneous vertebroplasty-treated osteoporotic vertebral compression fracture

The correlation between lower psoas mass and the prognosis of osteoporotic vertebral compression fractures (OVCF) is still unclear. This study aims to investigate the impact of lower psoas mass on the prognosis of patients undergoing percutaneous vertebroplasty (PVP). One hundred and sixty-three elderly patients who underwent single-segment PVP from January 2018 to December 2021 were included. The psoas to L4 vertebral index (PLVI) via MRI were measured to assess psoas mass. Patients were divided into high PLVI (> 0.79) and low PLVI (≤ 0.79) groups based on the median PLVI in the cohort. The basic information (age, gender, body mass index (BMI) and bone mineral density (BMD)), surgical intervention-related elements (duration of operation, latency to ambulation, period of hospital stay, and surgical site), postoperative clinical outcomes (Visual Analog Scale (VAS) scores, Oswestry Disability Index (ODI) scores, Japanese Orthopaedic Association (JOA) scores), and incidence of secondary fractures) were compared. Patients showed no statistically significant differences in terms of age, gender, surgical sute, BMI, BMD and preoperative VAS, ODI, JOA scores (P > 0.05) between the two groups. However, there were significant differences in terms of latency to ambulation, period of hospital stay (P < 0.05). VAS, ODI, and JOA scores at 1, 6, and 12 months after surgery showed that the high PLVI group had significantly better outcomes than the low PLVI group (P < 0.05). Additionally, the low PLVI group had a significantly higher incidence of recurrent fracture (P < 0.05). Lower psoas mass can reduce the clinical effect of PVP in patients with osteoporotic vertebral compression fractures, and is a risk factor for recurrent vertebral fracture.


Consent to participate
Informed consent was obtained from all individual participants included in the study.

Radiological assessment
All measurements were performed by the same two researchers who received professional training independently and repeated three times.MRI scans were conducted using the same protocol for all patients, with measurements taken at the level below the upper endplate of L4.The contours of the left and right psoas muscles and vertebrae were manually outlined on T2-weighted axial images using the Picture Archiving and Communication System (PACS) of the hospital.Image J software (U.S. National Institutes of Health, Bethesda, MD, USA) was used to evaluate the MR images to obtain the psoas to L4 vertebral index (PLVI), which represents the ratio of the bilateral psoas cross-sectional area (PCSA) at the level below the upper endplate of L4 to the vertebral body.The PLVI value at the 50th percentile was determined, and patients were classified into two groups based on their relationship to the median of the cohort: high PLVI (> 0.79) and low PLVI (≤ 0.79).(Fig. 1).

Surgical procedure
Percutaneous vertebroplasty (PVP) was consistently executed by the designated medical team.In brief, the patient was positioned prone on the operating table.Following standard aseptic protocol, the procedural area was disinfected, draped, and locally anesthetized.A 4-mm skin incision was then precisely created at the intended site overlying the facet joints on either side of the afflicted vertebral segment.Utilizing a specialized 2.5-mm diameter puncture needle, the operator navigated through the vertebral pedicle to access the core of the fractured vertebral body.Upon establishing a viable channel, a controlled volume of 3-5 ml of polymethylmethacrylate bone cement was incrementally injected into the vertebral body.Verification of the accurate placement and containment of the cement within the vertebral body was ascertained under the vigilant guidance of C-arm fluoroscopy.Following a requisite 8-min interlude for cement hardening, the puncture needle was withdrawn.The procedure culminated with the suture of the incision, followed by the application of sterile dressings.Postoperative anti-osteoporosis treatment includes the use of zoledronic acid for each patient during hospitalization, as well as daily foundational supplements of calcium and vitamin D upon discharge.

Statistical analysis
Data underwent statistical evaluation using SPSS 24.0 (IBM Corp., Armonk, NY, USA), with all values delineated as means ± standard deviation (SD).The study's focal point was the incidence rate of successive osteoporotic vertebral fractures, designated as the dependent variable.The independent variables encompassed demographic factors (age, gender, BMI, BMD), elements related to surgical intervention (duration of operation, latency to ambulation, period of hospital stay, and surgical site), alongside postoperative clinical indices (VAS, ODI, and JOA scores).Univariate analyses were performed employing Fisher's exact test for categorical data, and the Wilcoxon signed-rank test for continuous data, to elucidate differences between cohorts.A threshold of P < 0.05 was established for statistical significance.

Results
In this study, we encompassed a cohort of 144 patients with OVCF who fulfilled our inclusion criteria from a larger group of 163 individuals.The cohort was dichotomized into two groups: one with a higher PLVI comprising 72 patients, and another with a lower PLVI, also consisting of 72 patients.Comparative analysis revealed no statistically significant disparities in surgical segments, age, gender, operative duration, BMI, or BMD between the groups (Table 1).Nonetheless, a statistically significant acceleration in the time to ambulation and reduced hospital stay was noted in the high PLVI group (P < 0.05), indicating a quicker resumption of daily activities for these patients (Table 2).
Preoperative assessments of pain and functional status, measured via the VAS, ODI and JOA scores, did not differ significantly between the two groups (P > 0.05).However, at subsequent follow-ups post-surgery, the high PLVI group exhibited superior outcomes in VAS, ODI, and JOA scores (P < 0.05), corroborating a potential trend towards enhanced pain management and functional recovery in this subgroup (Table 3).

Complications
Within the cohort exhibiting a high percentage of lumbar vertebral involvement, a mere 2.78% (2 cases) reported persistent low back pain (LBP) at the final follow-up.In contrast, the group with a lower PLVI presented with 8.33% (6 cases) experiencing residual LBP.This disparity is statistically significant (P < 0.05).Alleviation of symptoms was partially attained through pharmacological intervention with anti-osteoporotic medication,  The statistical significance of this difference (P < 0.05) suggests a noteworthy correlation between lower psoas mass and the occurrence of SOVF (Fig. 2).

Discussion
The incidence of sarcopenia is notably elevated among elderly individuals, particularly accentuated within Asian demographics 17 .Some scholars use PLVI to represent central sarcopenia.Clinical evidence substantiates the correlation between PLVI and the prognosis of various geriatric ailments, thus garnering increasing favor among scholars 18 .Previous studies have shown a clear association between PLVI and adverse outcomes following liver transplantation and open repair of ruptured aortic aneurysm 19,20 .Our research discovered a correlation between PLVI and the surgical outcomes of OVCF patients, highlighting the potential of lower psoas mass as a prognostic indicator for elderly patients.The vast majority of OVCF patients undergo lumbar spine MRI preoperatively, providing measurement conditions early on.Additionally, assessing radiographic results in the early stages of patient hospitalization minimizes interference from other injuries or treatments, thus better reflecting the patient's baseline status.Through follow-up of cases within our group, we observed a correlation between lower psoas mass and OVCF.Osteoporosis and falls are predominant contributors to vertebral compression fractures among the elderly-falls represent external causative factors, while osteoporosis is an internal one.Contemporary research indicates a substantial interrelationship between sarcopenia and osteoporosis, which reciprocally exacerbate one another, culminating in detrimental consequences such as falls and fractures 21 .Sarcopenia is widely acknowledged as an independent risk factor for OVCF, impacting the prognosis distinct from osteoporosis 22 .Contrarily, some academics contend that sarcopenia, through its intimate association with osteoporosis, enhances the likelihood of OVCF, though it is not an independent risk factor 23 .Furthermore, falls is a significant risk factor for fragility fractures in the elderly, encompassing OVCF.Our study found that the two patient groups had similar levels of osteoporosis.Therefore, for the occurrence of re-fracture, the increased risk may be attributed more to lower psoas mass causing falls.We believe that lower psoas mass increases the risk of falls, consequently elevating the risk of fractures.Existing studies corroborate that lower PLVI elevates the risk of falls, thereby amplifying the risk of fractures 24 .An extensive study spanning 13,101 participants across five nations revealed that individuals with sarcopenia experienced a markedly elevated rate of fall-induced injuries and a 1.85-fold increase in fracture incidence due to falls when contrasted with non-sarcopenic counterparts 25 .Whether intensifying osteoporosis or augmenting the propensity for falls, sarcopenia invariably precipitates OVCF, the decline of physical function in the elderly, and an escalated risk of fractures.A separate investigation involving 120 patients, which assessed sarcopenia by measuring the lumbar muscle area, determined that a diminished area subsequent to muscle fat infiltration constituted an independent risk factor for recurrent fractures PVP surgery, irrespective of bone density.This correlation may stem from impaired balance due to muscle fat infiltration, thereby heightening the risk of recurrent fractures 26,27 .Furthermore, current studies propose that paravertebral muscles are vital in upholding spinal stability, as they inhibit excessive flexion and mitigate vertebral load.In the absence of muscular support, the spine's threshold for compression prior to flexion is a mere 2 kilograms 28 .Individuals with sarcopenia are bereft of this muscular defense, potentially precipitating repeated spinal compression fractures 29 .The debate continues over sarcopenia's influence on the postoperative prognosis in OVCF patients.Research encompassing 101 subjects indicates that muscle atrophy may compromise the clinical efficacy of PVP interventions 30 .Nevertheless, this assertion is not universally supported.An investigation involving 116 individuals receiving percutaneous kyphoplasty for vertebral fractures discerned no notable disparity in postoperative results between patients with and without sarcopenia 31 .Contrarily, additional research highlighted that sarcopenic patients experienced a significantly greater degree of persistent lower back pain following surgery, possibly attributed to minor micro-movements within the vertebrae subsequent to PVP 32 .In instances where lower back muscles are robust and potent, they can sustain spinal equilibrium.In contrast, muscles enfeebled by fatty degeneration fail to preserve vertebral stability, culminating in persistent lower back discomfort 33,34 .Bayram et al. disclosed that within a cohort of 103 OVCF patients undergoing PVP, those with sarcopenia (PVLI less than 0.603) faced a markedly increased mortality rate in comparison to their counterparts with a higher PVLI (43.1% vs 0%, P = 0.001) 35 .Such revelations underscore the clinically substantial ramifications of sarcopenia on the postoperative trajectory of OVCF patients treated with PVP.
This study pioneers the assessment of the correlation between psoas mass, as measured by the PVLI, and postoperative outcomes in patients undergoing PVP.The findings reveal notable deficiencies in lower psoas mass patients, both regarding alleviation of postoperative pain and the frequency of subsequent fractures.These observations are in harmony with the majority of existing literature on the subject.In light of these insights, it is recommended that patients presenting with lower psoas mass receive thorough evaluations in the domains of rehabilitation medicine and nutrition during the perioperative phase.The focus should be on optimizing nutritional status and fortifying muscle integrity.Furthermore, in the postoperative rehabilitation phase, there should be an emphasis on lumbar muscle exercises to augment muscle strength and mitigate muscle atrophy.Despite our findings, this study has several limitations.Given our relatively small sample size, we aim to gather more case data in the future.The median PLVI cutoff of 0.79, which led us to divide the cohort into "high" and "low" PLVI groups, may not be effective in other populations.Further collaboration with larger cohorts may help clarify this issue.Additionally, parameters such as sagittal balance and the efficacy of osteoporosis treatment were not included in our subsequent evaluations, which represents another avenue for future research.

Conclusion
Our investigation utilized MR imaging to measure psoas mass through the PVLI, affirming its deleterious effects on postoperative functional recuperation and the heightened likelihood of recurrent fractures in patients with OVCF treated with PVP.We advocate for the standard application of this imaging modality in the preoperative evaluation of OVCF sufferers to diminish the rate of recurring fractures and curtail postoperative complications via proactive interventions.

Figure 2 .
Figure 2. Typical re-fracture case of central sarcopenia, a 72-year-old female patient.On April 25, 2019, fall caused back pain, and then DR (A), MR (B, C) were performed.After admission, PVP was performed, and DR Was reexamined after operation (D).Five months later, low back pain recurred, and a reexamination of MR revealed a L4 fracture (E).The patient was readmitted for PVP (F).

Table 1 .
Surgical segmental division in two groups.

Table 2 .
Comparison of baseline data between the two groups.BMI indicates body mass index, BMD indicates bone mineral density, PLVI indicates psoas to L4 vertebral index.

Table 3 .
Comparisons of clinical outcomes between the two groups.VAS indicates Visual Analog Scale, ODI indicates Oswestry Disability Index and JOA indicates Japanese Orthopaedic Association.